Research area 1

Reduced sulfur moieties, i.e. sulfhydryl groups, are crucial for redox signaling and detoxification of reactive oxygen species in cells. The cysteine-containing tripeptide glutathione is a central player in these processes in nearly all living cells. We could show that in plants the partitioning on reduced sulfur between glutathione-mediated processes and protein translation are a prerequisite of thiol-based regulatory redox functions and control of reactive oxygen species for stress defense. Or in brief: the decision between growth and survival. The key component in this context is cysteine, the first stable organic sulfur compound in the assimilation pathway. Using HPLC and isotope detection, labeling experiments under steady state conditions showed that substantial amounts of cysteine can be partitioned between glutathione and proteins. Shifts between both destinations could be demonstrated by the analysis of knock-down mutants of Arabidopsis impaired in either glutathione synthesis (cad2-1) or sulfate reduction (sir1-1) or crosses thereof. The complementation of reduced growth phenotypes proved the principle of differential channeling of these two major routes. Targeting reduced sulfur preferentially to glutathione or the protein fraction even affected the redox state in chloroplast and cytosol as shown by live cell imaging with compartment-specific redoxGFP2 probes (Fig. 1).